Various systems are known for determining the tilt angle or tipping angle of a motor vehicle. For example, German Patent Publication 42 17 247 A1 discloses a system for monitoring the tilt of a motor vehicle, which is intended to prevent the over-turning or tipping-over of the vehicle as a result of a non-uniform loading of the loading surface of the vehicle. A measuring feeler or sensor determines the lengthwise tilt and the crosswise tilt of the vehicle relative to the vertical. The measured values are further processed in an electronic circuit, and the magnitude and direction of the tilt of the vehicle are displayed on a suitable display unit. The measuring unit can also be used for determining acceleration forces, and particularly crosswise accelerations of the vehicle, which can be a decisive factor affecting the driving stability of the vehicle. In this context, the measuring feeler or sensor acts as a centrifugal pendulum sensor.
In the above described known system it is disadvantageous that the true or actual tilting angle and tilting tendency of the vehicle cannot be determined using such a pendulum sensor. Namely, the pendulum sensor is only able to measure tilt angles relative to the apparent vertical, which does not always correspond to the true vertical, because the apparent vertical will be influenced by centrifugal forces that arise while the vehicle is driving around a curve, for example.
Various different apparatus, for example those using a rotation rate sensor such as a yaw rate sensor are also known for detecting the angular velocity and especially the rotation velocity about the lengthwise axis of the vehicle. Such apparatus are typically used as roll-over sensor systems which trigger a safety system such as a deployable roll bar or an airbag when the rotational velocity about the lengthwise axis of the vehicle reaches a maximum allowable value. For example, German Patent Publication 195 00 800 A1 discloses a system including a Coriolis rotation rate sensor including a seismic mass which is spring-supported on a substrate and which is therefore deflectable as a result of acceleration influences, as well as evaluation circuitry for determining a corresponding Coriolis acceleration. It is a disadvantage in such systems that only the magnitude of the angular velocity, i.e. the rotation velocity about the tilt axis, is determined. Once the magnitude of the rotation velocity has reached or exceeded a critical maximum value, a safety system is triggered. The system does not provide an advance warning to the driver of the vehicle, in sufficient time for the driver to take actions to avoid the rollover danger. Thus, the driver cannot actively counteract an imminent rollover condition, nor can a potentially dangerous loading condition of the vehicle be recognized, indicated and corrected before it results in a rollover condition, using such a system. Moreover, such systems cannot carry out a determination of the mass of the vehicle.